This invention relates to a swash-plate type compressor for compressing a refrigerant or the like, and more particularly to improvements in a lubricating oil feed system provided in such type compressor and employing no oil pump.
A swash-plate type compressor in general is constructed such that pistons are reciprocally moved within cylinder bores in unison with rotation of a swash plate obliquely secured on a drive shaft, to perform compressing actions in cooperation with suction valves and discharge valves. The drive shaft and the swash plate are rotatably supported by thrust bearings which are disposed to bear thrust loads as well as by radial bearings which are disposed to bear radial loads.
Such conventional swash-plate type compressor was provided with a lubricating oil feed system of the so-called "oil pump type" for supplying lubricating oil to the the thrust bearings and the radial bearings, which comprises an oil pump mounted at an end of the drive shaft and operable during rotation of the drive shaft to force lubricating oil from an oil sump provided below the swash plate chamber and feed it to the bearings through an oil feeding passageway extending in the drive shaft along its axis. However, the oil pump is rather expensive and requires special power to drive same. For this reason, lubricating oil feed systems without such an oil pump have recently been employed.
These conventional pumpless type systems include a differential pressure type. According to this type, lubricating oil in the oil sump below the swash plate chamber is splashed upwardly into oily mist by the outer fringe of the swash plate during its rotation so that refrigerant with the oily mist entrained therein is guided, due to a pressure difference between the swash plate chamber and low pressure chambers in the compressor, through oil feeding passageways leading to the low pressure chambers through the thrust bearings, the gap between the drive shaft and the cylinder block and the radial bearings. The above pressure difference between the swash plate chamber and the low pressure chamber is produced by a plenum caused by blow-bye gas introduced into the swash plate chamber through the gaps between the pistons and the cylinder bores during the discharge strokes of the pistons. Therefore, when the amount of such blow-bye gas produced is still small, namely, at the start of the compressor of during low speed operation thereof, a sufficient pressure difference is not obtained between the swash plate chamber and the low pressure chambers. Further, as known, the thrust bearings rotate about their own axes as the drive shaft, which is supported by them, rotates so that during high speed operation oily mist undergoes large flow resistance immediately before passing the thrust bearings due to centrifugal force caused by the rotation of the thrust bearings. owing to these facts, the conventional differential pressure type oil feed system is not capable of feeding a sufficient amount of lubricating oil to the bearings, particularly to the radial bearings on the above-mentioned occasions.